160 research outputs found

    Optical Fiber High Temperature Sensor Instrumentation for Energy Intensive Industries

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    Fibre optic pressure sensors in healthcare applications

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    This PhD thesis provides an extensive description of the development of two fibre optic pressure sensors for applications in health care: (i) a miniature fibre optic Fabry–Perot pressure sensor for fluid pressure measurements in invasive blood pressure monitoring and; (ii) a highly sensitive fibre Bragg grating sensor for contact/interface pressure measurement. The fibre optic Fabry-Perot pressure sensor has a diameter of 125 μm and is created by forming a cavity at the tip of a single-mode optical fibre. Parylene films were used as the pressure-sensitive diaphragm. The performance of three sensors with different aspect ratios has been investigated. The pressure sensing range of ~10 kPa (diastolic pressure)- ~15 kPa (systolic pressure) was targeted; sensor with the cavity of 70 μm in diameter and cavity length of 87 μm is able to sense within a range of 0- 18 kPa with an average sensitivity of 0.12 nm/kPa and response time of 3 seconds. The temperature sensitivity of 0.084 nm/°C was observed. Hysteresis and wavelength drift were observed for the sensors, which may be due to the permeability of the Parylene film to the air. Solutions for reducing hysteresis, wavelength drift and temperature cross-sensitivity are discussed in detail. Fibre Bragg grating (FBG) sensor technology is an ideal candidate for contact pressure measurement in compression therapy, pressure ulcer or prosthetics due to its many advantages such as conforming to body parts, small size, biocompatibility and multiplexing capabilities. A successful mathematical model for an FBG contact pressure sensor for healthcare applications has been presented and experimentally validated. The model has been compared with previous studies reported in the literature and takes into account birefringence. The highest sensitivity was achieved for the disc shape with a sensitivity of 0.8719 nm/MPa for a diameter of 5.5 mm, thickness of 1 mm and Young’s modulus of 20 MPa. This sensor was comprised of a 3 mm long FBG 6 centrally located in the patch. This is a pressure sensitivity of ~270 times increase when compared with a bare FBG reported in the literature. Birefringence effect was observed for the disk patch for pressures larger than 2.6 MPa. Even though FBGs provide high sensitivity in contact pressure sensing in healthcare, the potential applications are limited by the size and cost of commercially available FBG interrogators. A successful first attempt towards the development of a single channel compact FBG interrogation was accomplished. The system consists of a three-section distributed Bragg Reflector (DBR) tuneable laser, microcontroller unit, precision 5 channel current driver IC, photodiode circuit and a temperature controller IC. The tuneable laser was calibrated within 1535-1544 nm wavelength range to produce three current–wavelength lookup tables for wavelength resolution of 1 nm, 0.1 nm, 0.01 nm which is dependent on the current resolution. Futureworkincludesaddingpowercircuitry, a photodiode circuit and a feedback circuit to minimize power fluctuations. The system was tested compared to the commercial Smartscope FBG interrogator

    Fibre optic pressure sensors in healthcare applications

    Get PDF
    This PhD thesis provides an extensive description of the development of two fibre optic pressure sensors for applications in health care: (i) a miniature fibre optic Fabry–Perot pressure sensor for fluid pressure measurements in invasive blood pressure monitoring and; (ii) a highly sensitive fibre Bragg grating sensor for contact/interface pressure measurement. The fibre optic Fabry-Perot pressure sensor has a diameter of 125 μm and is created by forming a cavity at the tip of a single-mode optical fibre. Parylene films were used as the pressure-sensitive diaphragm. The performance of three sensors with different aspect ratios has been investigated. The pressure sensing range of ~10 kPa (diastolic pressure)- ~15 kPa (systolic pressure) was targeted; sensor with the cavity of 70 μm in diameter and cavity length of 87 μm is able to sense within a range of 0- 18 kPa with an average sensitivity of 0.12 nm/kPa and response time of 3 seconds. The temperature sensitivity of 0.084 nm/°C was observed. Hysteresis and wavelength drift were observed for the sensors, which may be due to the permeability of the Parylene film to the air. Solutions for reducing hysteresis, wavelength drift and temperature cross-sensitivity are discussed in detail. Fibre Bragg grating (FBG) sensor technology is an ideal candidate for contact pressure measurement in compression therapy, pressure ulcer or prosthetics due to its many advantages such as conforming to body parts, small size, biocompatibility and multiplexing capabilities. A successful mathematical model for an FBG contact pressure sensor for healthcare applications has been presented and experimentally validated. The model has been compared with previous studies reported in the literature and takes into account birefringence. The highest sensitivity was achieved for the disc shape with a sensitivity of 0.8719 nm/MPa for a diameter of 5.5 mm, thickness of 1 mm and Young’s modulus of 20 MPa. This sensor was comprised of a 3 mm long FBG 6 centrally located in the patch. This is a pressure sensitivity of ~270 times increase when compared with a bare FBG reported in the literature. Birefringence effect was observed for the disk patch for pressures larger than 2.6 MPa. Even though FBGs provide high sensitivity in contact pressure sensing in healthcare, the potential applications are limited by the size and cost of commercially available FBG interrogators. A successful first attempt towards the development of a single channel compact FBG interrogation was accomplished. The system consists of a three-section distributed Bragg Reflector (DBR) tuneable laser, microcontroller unit, precision 5 channel current driver IC, photodiode circuit and a temperature controller IC. The tuneable laser was calibrated within 1535-1544 nm wavelength range to produce three current–wavelength lookup tables for wavelength resolution of 1 nm, 0.1 nm, 0.01 nm which is dependent on the current resolution. Futureworkincludesaddingpowercircuitry, a photodiode circuit and a feedback circuit to minimize power fluctuations. The system was tested compared to the commercial Smartscope FBG interrogator

    Fabrication of wavelength division multiplexed in-fibre Bragg grating arrays for structural monitoring applications

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    Wavelength division multiplexed arrays of in-fibre Bragg gratings (IFBGs) are fabricated in hydrogen loaded optical fibres. The IFBG arrays are embedded into a carbon fibre composite test beam for the purpose of quantitative dc strain sensing. A near-field phase mask writing technique is compared to a conventional mirror interferometer and a novel phase mask based interferometer writing scheme. The combination of a wavelength tuneable UV source and a phase mask based interferometer offers, either a large spectral coverage of 51nm, or a laser limited Bragg wavelength accuracy of 0.03nm in the 800nm spectral region. The characteristics of gratings fabricated using these schemes are discussed. The axial strain sensitivity of optical fibre is investigated in a preliminary experiment. A three point bend test is then used to compare the theoretical strain applied to a carbon fibre test beam with measurements made by electrical strain gauges and embedded IFBG sensors over the range ±3400pstrain. A residual tensile strain results from embedding and is generally measured to be >2000pstrain. The majority of IFBG sensors appear well bonded to the surrounding host material and, with one exception, the strain responses of uncoated IFBG sensors deviate from the theoretically predicted values by <4.3%. A buffer coat around the sensor reduces the strain response by ~4% but does not affect its linearity or reproducibility. A spliced IFBG pair is used to separate strain and temperature measureands. A transfer matrix for the scheme is experimentally determined that has a calculated condition number of 23. The technique is compared to other reported methods of strain and temperature separation. Also, a demodulation scheme for IFBG sensors based on a volume holographic filter formed in photorefractive BaTi03 is reported. The filter has a strain measurement range of 2500pstrain, with a minimum detectable strain of 4pstrain/VHz.Ph

    Long-term stability tests of intrinsic Fabry-Perot optical fibre sensors at high temperatures

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    The main aim of this thesis is to develop and gain a better understanding of intrinsic Fabry-Pérot optical fibre sensors in high temperature environments. This thesis will describe the characteristics, manufacturing process, and applications of intrinsic Fabry-Pérot optical fibre sensors and their suitability for temperature sensing in high temperature environments. Intrinsic Fabry-Pérot optical fibre sensors with different types of sensing elements were manufactured and investigated throughout this project. The types of sensors differ at the dopant of their Fabry-Pérot cavity (sensing element), such as Gedoped core, F-doped depressed cladding and pure SiO2. Their long-term phase stability response at temperatures up to 1150oC over up to 4 months continuously monitoring is presented. Most promising results were given by pure SiO2 sensors up to 1000oC with a minimum temperature drift of less than 1oC. Above that temperature, all types of sensors showed temperature drifts from 20oC up to 100oC due to permanent changes of the core refractive index. At elevated temperatures, permanent changes of the core refractive index arise due to dopant diffusion in the optical fibre sensor, from core to cladding and vice versa, as well as tapering phenomena leading to phase response drifting and modulated behaviours. The presence of dopant in the Fabry-Pérot cavity proved to affect the phase stability of the sensors, especially for temperatures above 1000°C. An investigation of how dopant diffusion affects the core radius by making it larger is presented in this thesis as well. Using Scanning Electron Microscopy (SEM) coupled with Energy Dispersive X-ray (EDX) Spectroscopy, optical fibre sensors tested at temperatures up to 1150°C over long periods are investigated for dopant diffusion. After 85 days at temperatures above 900°C, germanium concentration in the core of the sensor has been dropped down to the 60% of its initial dopant concentration. Through calculations of FWHM and germanium wt. % concentration, the 40% of germanium dopant that have been diffused towards the cladding expanded the core radius by 0.9μm. This can lead to expanding tapering phenomena along the optical fibre and transformation of the single mode core to a multimode core, for specific wavelengths. Also, a modelled theoretical analysis of a 2nd order mode cavity interference in the fundamental cavity has been conducted proving its correlation with the modulated phase response at high temperatures.EPSR

    Intrinsic Fibre Strain Sensor Interrogation Using Broadband Interferometry

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    Strain measurement is an essential part of quality control and monitoring for many engineering purposes. One of the best types of strain sensors is a fibre optic strain sensor. Optical fibre sensors have the exclusive upper hand and unique features compared to more traditional sensors, which make them very enticing for various purposes, notably those with demanding conditions where other conventional electrical sensors normally fail. Due to the harsh environment, explosion risks, durability, and massive electromagnetic noises, well-known electrical sensors are impermissible in numerous technical and industrial applications. The fibre optic sensors can endure severe conditions (pressure, high temperature) and offer complete electromagnetic immunity. Thus, fibre optic sensors are a viable alternative for these types of purposes. This thesis talks about: •What are the strain and different types of strain sensors? o Traditional mechanical and electrical strain sensors as well as some backgrounds to what a fibre optic is, and various kinds of fibre optic gauges. •The advantages and disadvantages of fibre optic gauges. •Different methods of fibre sensing and their modulation and demodulation techniques. o Various interferometry sensors and techniques like Michelson, Fabry-Perot, Mach-Zehnder and Sagnac. •Commercial research about the Fabry-Perot. o Choosing the Fabry-Perot (Intrinsic Fabry-Perot interferometer)sensor, its advantages over other fibre optic sensors. •Setting up the testing system and various test steps that were taken, such as building two plastic jigs for the test. •Data analysis of the system, signal processing (Takeda method), different cropping and filtration of the signal to achieve the slope, and consequently calculate the strain, error%, stability, and various sensor characteristics. •The conclusion explains the need for the research, how the test was done and what it achieved

    Fibre optic hydrogen sensing for long term use in explosive environments

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    Hydrogen is an explosive and flammable gas with a lower explosive limit of just 4% volume in air. It is important to monitor the concentration of hydrogen in a potentially hazardous environment where hydrogen may be released as a by-product in a reaction or used as a principal gas/liquid. A fibre optic based hydrogen sensor offers an intrinsically safe method of monitoring hydrogen concentration. Previous research studies have demonstrated a variety of fibre optic based techniques for hydrogen detection. However the long-term stability of the hydrogen sensor and interrogation system has not yet been assessed and is the focus of this study. In the case of sensor heads being permanently installed in-situ, they cannot be removed for regular replacement, making long-term stability and reliability of results an important feature of the hydrogen sensor. This thesis describes the investigation and characterisation of palladium coated fibre optic sensor heads using two designs of self-referenced refractometer systems with the aim of finding a system that is stable in the long term (~6 months). Palladium was the chosen sensing material owing to its selective affinity for absorbing hydrogen. Upon hydrogen absorption, palladium forms a palladium- hydride compound that has a lower refractive index and lower reflectivity than pure palladium. The refractometers measured the changes in the reflectivity to enable calculation of the concentration of hydrogen present. A low detection limit of 10ppm H2 in air was demonstrated, with a response time of 40s for 1000ppm H2 in air. A further aspect to sensor stability was investigated in the form of sensor heads that had a larger area for palladium coverage. Hydrogen induced cracking in palladium is a common failure mechanism. A hypothesis is presented that a larger sensor area can reduce the probability of catastrophic failure resulting from cracks, which may improve the predictability of the sensor’s performance. Two sensor head designs have been proposed – fibre with a ball lens at the tip and fibre with a GRIN lens at the tip, both of which potentially offer a larger area than the core of a singlemode optical fibre. The limit of detection and response times of the sensor heads were characterised in hydrogen. For long term stability assessment of the sensor head and the interrogation unit, the system was left running for a period of 1 to 4 weeks and the noise and drift in the system was quantified using an Allan deviation plot

    Contribution to the development of new photonic systems for fiber optic sensing applications

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    En este trabajo de doctorado se presentan nuevos sistemas y subsistemas de sensores de fibra óptica. Así, se proponen y desarrollan nuevas técnicas, componentes y tecnologías basadas en láseres de fibra con espejos distribuidos (random), fibras de cristal fotónico, estructuras de luz lenta, multiplexores de inserción y extracción (add and drop), conmutadores tele-alimentados por luz, reflectometría óptica tanto en el dominio del tiempo como de la frecuencia o filtros ópticos reconfigurables. También se han demostrado nuevas aplicaciones para estructuras de sensores tradicionales y técnicas de medida ya conocidas. Todas ellas dirigidas a la mejora del funcionamiento de los actuales transductores, redes de sensores y aplicaciones de monitorización de salud estructural. De este modo, y en primer lugar, se han desarrollado nuevos transductores puntuales. En concreto, dos sensores interferométricos basados en fibras de cristal fotónico y otro basado en una estructura resonante en anillo. También se han realizado diferentes redes de sensores utilizando OTDRs comerciales. Por un lado, se han multiplexado diferentes sensores utilizando una red en forma de bus y, por el otro, se ha interrogado de manera remota un sensor FLM/LPG a una distancia de 253 km sin necesidad de amplificación. Se han estudiado láseres basados en efecto de realimentación distribuida random (RDFB) para su uso en interrogación de sensores. Para ello, se han demostrado dos nuevos láseres multi-longitud de onda y también, por primera vez, se ha modulado un laser random. Después, se han demostrado experimentalmente varias redes de sensores de fibra óptica teniendo en cuenta los principales desafíos que estas presentan: multiplexar varios sensores en una misma red y permitir su monitorización de manera remota. En primer lugar, se han multiplexado sensores basados en la modulación de la intensidad óptica utilizando técnicas de multiplexación en dominio del tiempo. En segundo lugar, se han multiplexado sensores basados en fibras de cristal fotónico. En tercer lugar, se presentan tres nuevos métodos para la medida remota de sensores. Por último, se incluye la demostración de un conmutador de fibra óptica tele-alimentado a través de luz. Éste se utiliza en tres redes diferentes para añadir robustez e incrementar la versatilidad en la multiplexación. Finalmente, se han realizado tres pruebas de campo para aplicaciones de monitorización de salud estructural.In this PhD work, different new photonic systems and subsystems for fiber optic sensing are presented. The aim of this thesis has been to contribute to the fiber optic sensors field using modern techniques, components and technologies such as random fiber lasers, photonic crystal fibers, slow light structures, add and drop multiplexers, powered by light switches, optical frequency and time domain reflectometry or reconfigurable optical filters, among others. New applications of traditional sensing structures or techniques have been also demonstrated. All of them focused on improving the performance of current sensors transducers, multiplexing networks and structural health monitoring applications. Thus, new point transducers have been developed: two of them are interferometric sensors based on photonic crystal fibers; and another one is based on a fiber ring resonator structure. Fiber optic sensor networks using commercial OTDRs have been also explored. On the one hand, different sensors have been successfully multiplexed in the same bus network. And, on the other hand, a FLM/LPG sensor was remotely interrogated at a distance of 253 km without using amplification. Random distributed feedback (RDFB) lasers have been explored for sensors interrogation. Two multi-wavelength Raman fiber lasers suitable for sensors interrogation have been demonstrated. Also, a random fiber laser has been internally modulated for the first time. Then, some experimental demonstrations of fiber optic sensors networks have been carried out taking into account the principal challenges they pose: multiplexing a number of optical sensors in a single networks, and enabling the possibility of remote sensing. Firstly, intensity sensors using TDM technology have been multiplexed. Secondly, PCF sensors have been successfully multiplexed. Thirdly, three new approaches to enable remote sensing are presented. Finally, a remote powered by light fiber optic switch have been included in three networks in order to add robustness and multiplexing versatility.Este trabajo se ha llevado a cabo gracias a las aportaciones económicas recibidas de los siguientes organismos, entre otros: - Secretaría de Estado de Investigación, Desarrollo e Innovación, Ministerio de Economía y Competitividad de España a través del programa de Formación del Personal Investigador y asociado al proyecto de investigación TEC2010-20224-C02-01. - Universidad Pública de Navarra mediante las ayudas a tesis doctorares. - Acción Europea COST- TD1001: Novel and Reliable Optical Fibre Sensor Systems for Future Security and Safety Applications (OFSeSa) - También se ha recibido financiación del Proyecto de Investigación de la Secretaría de Estado de Investigación, Desarrollo e Innovación, Ministerio de Economía y Competitividad de España TEC2013-47264-C2-2-R, de Innocampus, del Proyecto Europeo SUDOE-ECOAL-Intereg Project ECOAL-MGT y de los Fondos FEDER.Programa Oficial de Doctorado en Tecnologías de las Comunicaciones (RD 1393/2007)Komunikazioen Teknologietako Doktoretza Programa Ofiziala (ED 1393/2007
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